Irrigated catheter with improved ablation tip electrode fluid distribution

ABSTRACT

A catheter has a two-piece tip electrode with a shell and a support structure defining a chamber, and a fluid distribution tube that extends longitudinally into the chamber, the fluid tube having fluid apertures along its length for distributing fluid more uniformly distributed throughout the chamber for improved cooling and thus minimizing the risk of char formation on regions of the tip electrode more prone to overheating.

FIELD OF INVENTION

The present invention relates to electrophysiologic (EP) catheters, inparticular, EP catheters for ablating cardiac tissue.

BACKGROUND

Ablation of cardiac tissue is well known as a treatment for cardiacarrhythmias. In radio-frequency (RF) ablation, for example, a catheteris inserted into the heart and brought into contact with tissue at atarget location. RF energy is then applied through electrodes on thecatheter to heat tissue to a destructive temperature in order to createa lesion for the purpose of breaking arrhythmogenic current paths in thetissue.

Irrigated catheters are now commonly used in ablation procedures.Irrigation provides many benefits including cooling of the electrode andtissue which prevents overheating of tissue that can otherwise causeadjacent blood to form char and coagulum. Irrigated tip electrodes areknown, including tip electrodes with a two-piece construction having aninner support structure and a dome shell mounted thereon. A cavity isformed between the support structure and the dome shell to provide aplenum chamber that enables a flow of fluid exiting the tip electrodevia fluid ports formed in the dome shell. However, irrigation fluid maynot be uniformly distributed throughout the plenum chamber and thus notall portions of the dome shell may receive uniform cooling. Withoutuniform cooling, hot spots may result which lead to char formationduring ablation.

Accordingly, it is desirable that a catheter with a plenum chamberreceive more consistent and evenly distributed irrigation cooling to allportions of the dome shell to minimize char formation. It is desirablefor the irrigation to reach proximal end portion of the dome shell andother regions with a lesser number of fluid exit ports in the domeshell.

SUMMARY OF THE INVENTION

A catheter has a tip electrode a shell and a support structure defininga fluid plenum chamber. The catheter advantageously includes a fluiddistribution tube that extends longitudinally into the chamber, whereinthe fluid distribution tube has fluid apertures along its length fordistributing fluid more uniformly throughout the chamber in improvedcooling and thus minimizing the risk of char formation on regions of thetip electrode more prone to overheating.

In some embodiments of the present invention, an electrophysiologiccatheter has an elongated catheter body, a control handle proximal ofthe catheter body, and a tip electrode distal of the catheter body, thetip electrode configured for irrigation and having a shell and a supportmember defining an internal chamber. The tip electrode includes a fluiddistribution tube that extends longitudinally into the chamber and has aside wall with a plurality of apertures.

In some detailed embodiments, the apertures in the side wall of thefluid distribution tube are arranged in a predetermined pattern.

In some detailed embodiments, the predetermined pattern includes adistal aperture and a proximal aperture.

In some detailed embodiments, the predetermined pattern includes theplurality of apertures are longitudinally aligned.

In some detailed embodiments, the predetermined pattern includes agreater spacing between more-proximal adjacent apertures and a lesserspacing between more-distal adjacent apertures in the longitudinaldirection.

In some detailed embodiments, the apertures have different sizes.

In some detailed embodiments, the apertures have different shapes.

In some detailed embodiments, the predetermined pattern includes theapertures having different radial positions in the side wall.

In some detailed embodiment, the catheter includes an irrigation tubingin fluid communication with the fluid distribution tube.

In some detailed embodiments, the internal chamber has a first lengthand the fluid distribution tube has a second length that ranges between0.5 and 0.9 of the first length.

In some detailed embodiments, at least one aperture is more proximalthan one or more most-proximal ports.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings. It isunderstood that selected structures and features have not been shown incertain drawings so as to provide better viewing of the remainingstructures and features.

FIG. 1 is a perspective view of catheter in accordance with anembodiment of the present invention.

FIG. 2 is an end cross-sectional view of a catheter body of the catheterof FIG. 1, taken along line A-A.

FIG. 3 is an end cross-sectional view of an intermediate section of thecatheter of FIG. 1, taken along line B-B.

FIG. 4 is side elevational view of a distal tip section of the catheterof FIG. 1.

FIG. 5 is a perspective illustration representative of various coils inthe distal tip section of FIG. 4.

FIG. 6 is a side-cross-sectional view of the tip electrode of FIG. 4.

FIG. 7 is an end cross-sectional view of the tip electrode of FIG. 5.

FIG. 8 is a side-elevational view of a fluid distribution tube, inaccordance with an embodiment of the present invention.

FIG. 9 is a side cross-sectional view of the fluid distribution tube ofFIG. 8.

FIG. 10 is a side cross-sectional view of a fluid distribution tube, inaccordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an embodiment of a catheter 10 with an improvedirrigation-cooled ablation tip electrode. The catheter has an elongatedcatheter body 12 with proximal and distal ends, an intermediatedeflectable section 14 at the distal end of the catheter body 12, and adistal section 15 with a tip electrode 17. The catheter also includes acontrol handle 16 at the proximal end of the catheter body 12 forcontrolling deflection (single or bi-directional) of the intermediatesection 14 relative to the catheter body 12.

With reference to FIG. 2, the catheter body 12 comprises an elongatedtubular construction having a single, axial or central lumen 18. Thecatheter body 12 is flexible, i.e., bendable, but substantiallynon-compressible along its length. The catheter body 12 can be of anysuitable construction and made of any suitable material. A presentlypreferred construction comprises an outer wall 20 made of polyurethaneor PEBAX. The outer wall 20 comprises an imbedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter body 12 so that, when the control handle 16 is rotated, theintermediate section 14 of the catheter 10 will rotate in acorresponding manner.

The outer diameter of the catheter body 12 is not critical, but ispreferably no more than about 8 french, more preferably 7 french.Likewise the thickness of the outer wall 20 is not critical, but is thinenough so that the central lumen 18 can accommodate puller members(e.g., puller wires), lead wires, and any other desired wires, cables ortubings. If desired, the inner surface of the outer wall 20 is linedwith a stiffening tube 22 to provide improved torsional stability. Adisclosed embodiment, the catheter has an outer wall 20 with an outerdiameter of from about 0.090 inch to about 0.94 inch and an innerdiameter of from about 0.061 inch to about 0.065 inch.

Components that extend between the control handle 16 and the deflectablesection 14 pass through the central lumen 18 of the catheter body 12.These components include lead wires 30T and 30R (for the tip electrode17 and a plurality of ring electrodes 21 proximal of the tip electrode),an irrigation tubing 38 with lumen 37 for delivering fluid to the tipelectrode, a cable 33 for a position sensor 34 carried in or near thedistal section 15, puller wires 32 a, 32 b for deflecting theintermediate section 14, and a pair of thermocouple wires 41, 42 tosense temperature at the distal section 15. It is understood that insome embodiments one of the wires 41 and 42 is configured as a lead wirefor delivering electrical energy to the tip electrode 17 in lieu of thelead wire 30T.

Illustrated in FIG. 3 is an embodiment of the intermediate section 14which comprises a short section of tubing 19. The tubing also has abraided mesh construction but with multiple lumens, for example off-axislumens 23, 26 a, 26 b and 27 and on-axis lumen 28. The lumen 27 carriesthe lead wires 30T and 30R, and the thermocouple wires 41 and 42. Thelumen 23 carries the position sensor cable 33. The lumen 28 carries theirrigation tubing 38. The lumen 26 a carries a puller wire 32 a fordeflection of the intermediate section. For bi-directional deflection,the diametrically-opposing lumen 26 b carries a second puller wire 32 b.

The tubing 19 of the intermediate section 14 is made of a suitablenon-toxic material that is more flexible than the catheter body 12. Asuitable material for the tubing 19 is braided polyurethane, i.e.,polyurethane with an embedded mesh of braided stainless steel or thelike. The size of each lumen is not critical, but is sufficient to housethe respective components extending therethrough.

Each puller wire 32 a and 32 b has a lubricious coating, e.g. ofTeflon®. The puller wires can be made of any suitable metal, such asstainless steel or Nitinol and the Teflon coating imparts lubricity tothe puller wire. The puller wire preferably has a diameter ranging fromabout 0.006 to about 0.010 inch.

As shown in FIG. 3, the portion of each puller wire in the catheter body12 passes through a compression coil 35 in surrounding relation to itspuller wire. Each compression coil 35 extends from the proximal end ofthe catheter body 12 to at or near the proximal end of the intermediatesection 14. The compression coils are made of any suitable metal,preferably stainless steel, and are tightly wound on themselves toprovide flexibility, i.e., bending, but to resist compression. The innerdiameter of the compression coil is preferably slightly larger than thediameter of the puller wire. Each portion of the puller wires distal ofthe compression coil 35 may extend through a respective protectivesheath 39 to prevent the puller wire from cutting into the tubing 19 ofthe intermediate section 14 during deflection.

Proximal ends of the puller wires 32 a and 32 b are anchored in thecontrol handle 16. Distal ends of the puller wires 32 a and 32 b areanchored in the distal section 15, as described further below. Separateand independent longitudinal movements of the puller wires relative tothe catheter body 12, which results in, respectively, deflection of theintermediate section 14 along a plane, are accomplished by suitablemanipulation of a deflection member of the control handle 16. Suitabledeflection members and/or deflection assemblies are described inco-pending U.S. Publication No. US2010/0168827 A1, published Jul. 1,2010, entitled DEFLECTABLE SHEATH INTRODUCER, and U.S. Publication No.US2008/0255540 A1, published Oct. 16, 2008, entitled STEERING MECHANISMFOR BI-DIRECTIONAL CATHETER, the entire disclosures of both of which arehereby incorporated by reference.

With reference to FIG. 4, at the distal end of the intermediate section14 is the distal tip section 15 that includes the tip electrode 17 and arelatively short piece of non-conductive connector tubing or covering 24between the tip electrode 17 and the intermediate section 14. In theillustrated embodiment, the connector tubing 24 has a single lumen 44which receives a distal end of the position sensor cable 33 and allowspassage of components including electrode lead wires 30T and 30R,thermocouple wires 41 and 42, and the irrigation tubing 38 into thedistal section 15 and tip electrode 17. The single lumen 44 of theconnector tubing 24 allows these components to reorient themselves asneeded from their respective lumens in the intermediate section 14toward their location within the distal section 15 and tip electrode 17.In the disclosed embodiment, the tubing 24 is a protective tubing, e.g.,PEEK tubing, having a length ranging between 6 mm and 12 mm, morepreferably about 11 mm.

The connector tubing 24 also houses a force sensor 90. Aspects of aforce sensor similar to force sensor are described in U.S. Pat. No.8,357,152, issued on Jan. 22, 2013 to Govari et al., entitled CATHETERWITH PRESSURE SENSING, and in U.S. Patent Publication No. 2011/0130648,to Beeckler et al., filed Nov. 30, 2009, entitled CATHETER WITH PRESSUREMEASURING TIP, both of whose disclosures are incorporated herein byreference.

With reference to FIG. 4 and FIG. 5, the force sensor 90 includes aresilient coupling member 60, which forms a spring joint. In someembodiments, the coupling member 60 has hollow tubular form with acentral lumen 68 therethrough. Coupling member 60 typically has one ormore helices cut or otherwise formed in the member, so that the memberbehaves as a spring. In some embodiments, the coupling member 60 isformed of a superelastic alloy, such as nickel titanium (Nitinol),within force sensor 90.

The force sensor 90 includes a joint sensing assembly comprising coils76, 78, 80 and 82 that provides accurate reading of any dimensionalchange in axial displacement and angular deflection in the spring joint,including when the tip electrode 17 is angularly displaced from alongitudinal axis 84 of the catheter, such as then the tip electrodecomes into contact with tissue. These coils are one type of magnetictransducer that may be used with the catheter. A “magnetic transducer,”in the context of the present patent application and in the claims,means a device that generates a magnetic field in response to an appliedelectrical current and/or outputs an electrical signal in response to anapplied magnetic field. Although the embodiments described herein usecoils as magnetic transducers, other types of magnetic transducers maybe used in alternative embodiments, as will be apparent to those skilledin the art.

The coils in the sensing assembly are divided between two subassemblieson opposite sides of the spring joint. One subassembly comprises coil 82distal of the spring joint, which is driven by a current, via a wire(included in the cable 33), to generate a magnetic field. This field isreceived by a second subassembly, comprising coils 76, 78 and 80, whichare located proximal of the spring joint, in a section of the connectortubing 24 that is spaced axially apart from and proximal of the coil 82.The term “axial,” as used in the context of the present patentapplication and in the claims, refers to a direction along or parallelto the longitudinal axis 84 of the catheter. The coil 82 typically lieson-axis with the longitudinal axis 84.

Coils 76, 78 and 80 are fixed in connector tubing 24 at the sameproximal distance from the coil 82 but at different radial locations.(The term “radial” refers to coordinates about the longitudinal axis84.) Specifically, in the illustrated embodiment, the coils 76, 78 and80 are all located in the same plane perpendicular to the longitudinalaxis 84 but at different equi-azimuthal angles about the longitudinalaxis 84, that is, the three coils are spaced azimuthally 120 degreesapart at the same axial distance from the coil 82 along the longitudinalaxis 84.

The coils 76, 78 and 80 generate electrical signals in response to themagnetic field transmitted by coil 82. These signals are conveyed bywires (part of the cable 33) extending proximally from the distalsection 15, through the lumen 23 of the intermediate section 14, throughthe lumen 18 of the catheter body 12 and into the control handle 16. Thesignals are processed by a remote processor in order, for example, tomeasure the axial displacement of spring joint along the longitudinalaxis 84, as well as to measure the angular deflection of the joint fromthe longitudinal axis 84. From the measured displacement and deflection,the processor is able to evaluate, typically using a previouslydetermined calibration table, a magnitude and a direction of the forceon the spring joint.

The same processor (or another processor) detects and measures thelocation and orientation of distal section 15. The method of measurementmay be by any convenient process known in the art. In one embodiment,magnetic fields generated external to a patient create electric signalsin elements in the distal section 15, and the processor uses theelectric signal levels to determine the distal section location andorientation. Alternatively, the magnetic fields may be generated in thedistal section 15, and the electrical signals created by the fields maybe measured external to patient. As shown in FIG. 4 and FIG. 5, theelements in distal section 12 that are used to position and locate thedistal section) 12 include orthogonal coil C_(x) aligned with the Xaxis, orthogonal coil C_(y) aligned with the Y axis, and one of the coil76, 78 and 80 (in addition to their use as elements of force sensor),for example, the coil 80 aligned with the Z axis as orthogonal coilC_(z). The coils C_(x), C_(y), C_(z)/80 are housed in the connectortubing 24, within the lumen 68 of the coupling member 60. These coilsare the sensing components of the electromagnetic position sensor 34 towhich the cable 33 is connected. In some embodiments, the catheterincludes a single axial sensor (SAS) cable assembly in lieu of the cable33 and the electromagnetic position sensor 34 for position and locationsensing. A SAS cable assembly suitable for use is described in U.S. Pat.No. 8,792,962, titled CATHETER WITH SINGLE AXIAL SENSORS, the entiredisclosure of which is incorporated herein by reference.

With reference to FIG. 6, the irrigated tip electrode 17 has a two-piececonstruction that includes an electrically-conductive dome shell 50 andan electrically-conductive internal support member or “plug” 52 whichjointly define a cavity of an internal plenum chamber 51 that issurrounded, enclosed and sealed by the shell 50 and the support member52. The chamber has a longitudinal length L extending between a distalface 52D of the plug 52 and a distal inner wall 51D. The shell 50 has ahollow cylindrical body 50B with an open proximal portion 50P and aclosed distal portion 50D adapted for tissue contact. The distal portion50D has a dome atraumatic distal end 53. Formed in shell wall 63 are aplurality of fluid exit ports 56 that allow fluid communication betweenthe chamber 51 and outside the shell 50.

The shell 50 and the plug 52 are constructed of a biocompatible metal,including a biocompatible metal alloy. A suitable biocompatible metalalloy includes an alloy selected from stainless steel alloys, noblemetal alloys and/or combinations thereof. In one embodiment, the shellis constructed of an alloy comprising about 80% palladium and about 20%platinum by weight. In an alternate embodiment, the shell 50 and themember 52 are constructed of an alloy comprising about 90% platinum andabout 10% iridium by weight. In some embodiments, the shell is formed bydeep-drawing manufacturing process which produces a sufficiently thinbut sturdy shell wall that is suitable for handling, transport throughthe patient's body, and tissue contact during mapping and ablationprocedures.

The lead/thermocouple wires 30T, 41 and/or 42 and the irrigation tubing31 pass proximally from the tip electrode 17 through a protective,nonconductive tubing 65 (FIG. 4). The wires and the irrigation tubingpass further through the lumens 27 and 28 of the tubing 19 of theintermediate section 14 and through the lumen 18 of the catheter body12. The shell 50 and the plug 52 facilitate the provision of a plenumcondition within the chamber 51; that is, where fluid is forced ordelivered in the chamber 51 and then passes through the exit ports 56formed in shell wall 63 to exit the tip electrode 17.

As shown in FIG. 7, the plug 52 has a plurality of holes. In theillustrated embodiment, the plug 52 has four blind holes, namely, 57 a,57 b and 58, on its proximal face 52P and one through-hole 61. The blindholes 57 a and 57 b are off-axis, diametrically opposed and generally inlongitudinal alignment with lumens 26 a and 26 b of the deflectablesection 14 for receiving and anchoring the puller wire 32 a and 32 b,respectively. One or more blind hole(s) 58 are off-axis and adapted toreceive and anchor distal ends of lead wire 30T and thermocouple wires41 and 42. As mentioned, in some embodiments, one of the thermocouplewires 41 and 42 is configured as a lead wire for the tip electrode 17,obviating the need for the separate lead wire 30T. The through-hole 61is on-axis and adapted to receive a distal portion of the irrigationtubing 38.

As shown in FIG. 6, extending through the through-hole 61 from a distalface 52D of the plug 52 is an elongated hollow fluid distribution tube100 formed with a plurality of graduated fluid distribution apertures101 arranged in a predetermined pattern. The fluid tube 100 extendslinearly and distally into the chamber 51, on-axis with the longitudinalaxis 84 of the catheter. The fluid tube 100 has a closed distal end.Center lumen 102 of the fluid tube 100 is in communication with thelumen 37 of the irrigation tubing 38 and also with the fluid apertures101 formed in side wall 103 of the fluid tube 100. Advantageously, thelumen 102 of the fluid tube 101 in the chamber 51 reaches deep into thechamber by extending distally toward the distal end 51D of the chamber51 and having a length LF ranging between about 0.5 and 1.0, morepreferably about 0.6 and 0.8, of the length L of the chamber 51, wherethe side wall 103 of the fluid tube 101 is configured with the fluidapertures 101 in a predetermined pattern. The pattern includes, forexample, fluid apertures 101 spanning along the length of the fluid tube100, so that there is at least one proximal aperture 101P and at leastone distal aperture 101D, each occupying a different longitudinalposition in the fluid tube 100, as show in FIG. 8. Moreover, the sizeand/or shape of each aperture 101 may vary. In the embodiment of FIG. 9,the fluid tube 100 includes eight apertures: four pairs ofdiametrically-opposed apertures, with two smaller-sized, most-distalapertures 101D, two smaller-sized, most-proximal apertures 101P, and twolarger-sized, mid-apertures therebetween 101M. The spacing S1 and S2 andS3 between adjacent apertures differs, for example, where a more-distalspacing is lesser than a more-proximal spacing, or where S1<S2<S3. Insome embodiments, the fluid apertures 101 are longitudinally aligned,occupying similar radial positions in the side wall 103, as shown inFIG. 8 and FIG. 9. In some embodiments, longitudinally-adjacentapertures 101 occupy different radial positions in the side wall 103,for example, apertures 101A are 90 degrees radially offset fromapertures 101B, as shown in FIG. 10.

In some embodiments, at least some of the apertures 101 are sizedsmaller than the ports 56 of the shell 50. In some embodiments, at leastsome of the apertures 101 are sized about the same as the ports 56. Insome embodiments, at least some of the apertures 101 are sized largerthan the ports 56. In some embodiments, at least one of the apertures101 is more proximal than the most proximal port(s) 56.

The configurations of the apertures 101 spanning along the length of thefluid tube 100 advantageously provide predetermined distributionpatterns of irrigation fluid to both the proximal and distal portions ofthe chamber 51 which provide better cooling of the tip electrode 17regardless of the configuration of the exit ports 56 in the wall 63 ofthe shell 50. Thus, in the portion(s) of the shell 50 are lacking ordevoid of exit ports 56, e.g., the proximal portion of the shell 50 nearthe plug 52 (see “x” in FIG. 6), the fluid tube 100 and its apertures101 enable improved circulation of cooling fluid within the chamber 51,in contrast to prior plenum chamber where irrigation fluid enters thechamber 51 merely at its proximal end without other mechanisms or forcesthat delivers fluid more uniformly throughout the entirety of thechamber. The different sizing and/or shape of the apertures 101 enablethe fluid to enter the chamber 51 at different velocities for improvingcirculation within the chamber 51. Improved circulation improves coolingof all portions of the tip electrode 17 and thus decrease the risk ofchar formation on all portions of the tip electrode, especially theproximal portion of the tip electrode and portions lacking or devoid ofexit ports. By applying computation fluid dynamics (CFD) to variationsin tip electrode parameters, including, for example, dome shell/chambersize, the plurality, location, shape and/or size of exit ports 56 in theshell 50, the relative length of the fluid tube 100 to the chamberlength, the plurality location, shape and/or size of apertures 101,fluid dynamics within the tip electrode 17 are calculated and readilyadjusted, as desired or appropriate.

It is understood that the fluid tube 100 may be constructed as a portionof the irrigation tubing 38, for example, of a similar material, as aproximal portion of the irrigation tubing. Alternatively, the fluid tube100 may be constructed of a different material and/or as a separate ordifferent component from the irrigation tubing, with fluid communicationenabled by the through-hole 60 in the plug 52, or by another fluidtubing. In any case, the fluid tube 100 is constructed for fluidcommunication between its lumen 102 and the lumen 37 of the irrigationtubing 38, either directly or indirectly, such that fluid is passed anddelivered between the irrigation tubing 38 and the fluid tube 100.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. Notably, the drawings are not necessarily to scale, andany one or more features of an embodiment may be included in any otherembodiment in addition to or in lieu of any feature, as desired orappropriate. Accordingly, the foregoing description should not be readas pertaining only to the precise structures described and illustratedin the accompanying drawings, but rather should be read consistent withand as support to the following claims which are to have their fullestand fair scope.

What is claimed is:
 1. An electrophysiologic catheter having: anelongated catheter body; a control handle proximal of the elongatedcatheter body; and a tip electrode distal of the elongated catheterbody, the tip electrode configured for irrigation and comprising: ashell comprising a generally cylindrical proximal body, and a distal endconfigured to contact tissue, the shell comprising an internal cavityand a plurality of radially spaced apart generally circular side portsin the generally cylindrical proximal body and one or more end ports inthe distal end, each of the plurality of generally circular side portsand the one or more end ports extending from the internal cavity througha shell wall to outside the shell; a support member, the shell and thesupport member defining the internal cavity, a proximal shell portion ofthe shell that is distal of a distal end of the support member beingdevoid of any side ports; and a fluid distribution tube extendingthrough the support member longitudinally into the internal cavity, thefluid distribution tube having a side wall with a plurality of aperturesin fluid communication with the internal cavity, at least one of theplurality of apertures of the fluid distribution tube being moreproximal than a most-proximal one of the plurality of generally circularside ports of the shell such that the at least one of the plurality ofapertures that is more proximal than the most-proximal one of theplurality of generally circular side ports of the shell is in fluidcommunication with the proximal shell portion that is devoid of any sideports, and at least one other of the plurality of apertures of the fluiddistribution tube being distal of the most-proximal one of the pluralityof generally circular side ports of the shell, the at least one of theplurality of apertures that is more proximal than the most-proximal oneof the plurality of generally circular side ports of the shell having asmaller size than at least one other of the plurality of apertures thatis distal of the at least one of the plurality of apertures that is moreproximal than the most-proximal one of the plurality of generallycircular side ports of the shell.
 2. The catheter of claim 1, whereinthe plurality of apertures of the fluid distribution tube are arrangedin a predetermined pattern.
 3. The catheter of claim 2, wherein thepredetermined pattern includes longitudinal alignment of the pluralityof apertures.
 4. The catheter of claim 2, wherein the predeterminedpattern includes a greater spacing between more-proximal adjacentapertures and a lesser spacing between more-distal adjacent apertures.5. The catheter of claim 2, wherein the predetermined pattern includesthe plurality of apertures having different radial positions in the sidewall of the fluid distribution tube.
 6. The catheter of claim 2, whereinthe predetermined pattern of the plurality of apertures of the fluiddistribution tube comprises: one first pair of proximal apertures thatare diametrically opposed and longitudinally aligned, two second pairsof middle apertures, each of the middle apertures of each of the twopairs of middle apertures being diametrically opposed and longitudinallyaligned, and one third pair of distal apertures that are diametricallyopposed and longitudinally aligned, the first pair of proximal aperturesbeing proximal of the second pairs of middle apertures, and the secondpairs of middle apertures being proximal of the third pair of distalapertures, a first spacing between the first pair of proximal aperturesand proximal-most pair of the two pairs of middle apertures beinggreater than a second spacing between the two pairs of middle apertures,and the second spacing between the two pairs of middle apertures beinggreater than a third spacing between the third pair of distal aperturesand a distal-most pair of the two pairs of middle apertures.
 7. Thecatheter of claim 1, wherein the plurality of apertures of the fluiddistribution tube have different sizes.
 8. The catheter of claim 1,wherein the plurality of apertures of the fluid distribution tube havedifferent shapes.
 9. The catheter of claim 1, further comprising anirrigation tubing in fluid communication with the fluid distributiontube.
 10. The catheter of claim 1, wherein the internal cavity has afirst length and the fluid distribution tube extends into the internalcavity by a second length that ranges between 50% and 100% of the firstlength.
 11. The catheter of claim 1, wherein the internal cavity has afirst length and the fluid distribution tube extends into the internalcavity by a second length that ranges between 60% and 80% of the firstlength.
 12. An electrophysiologic catheter having: an elongated catheterbody; a control handle proximal of the elongated catheter body; and atip electrode distal of the elongated catheter body, the tip electrodeconfigured for irrigation and comprising: a shell comprising an internalcavity and comprising a generally cylindrical proximal body, a distalend configured to contact tissue, a plurality of radially spaced apartgenerally circular side ports in the generally cylindrical proximalbody, and one or more end ports in the distal end, each of the pluralityof generally circular side ports and the one or more end ports extendingfrom the internal cavity through a shell wall to outside the shell; asupport member, the shell and the support member defining the internalcavity, a proximal shell portion of the shell that is distal of a distalend of the support member being devoid of any side ports; and a fluiddistribution tube extending through the support member longitudinallyinto the internal cavity, the fluid distribution tube having a side wallwith a plurality of apertures in fluid communication with the internalcavity, one or more of the plurality of apertures having a sizedifferent than one or more of either the one or more end ports or theplurality of generally circular side ports of the shell, and at leastone of the plurality of apertures of the fluid distribution tube beingmore proximal than a most-proximal one of the plurality of generallycircular side ports of the shell such that the at least one of theplurality of apertures that is more proximal than the most-proximal oneof the plurality of generally circular side ports of the shell is influid communication with the proximal shell portion that is devoid ofany side ports, and at least one other of the plurality of apertures ofthe fluid distribution tube being distal of the most-proximal one of theplurality of generally circular side ports of the shell, the one or moreof the plurality of apertures that is more proximal than themost-proximal one of the plurality of generally circular side ports ofthe shell having a smaller size than at least one other of the pluralityof apertures that is distal of the one or more of the plurality ofapertures that is more proximal than the most-proximal one of theplurality of generally circular side ports of the shell.
 13. Thecatheter of claim 12, wherein the internal cavity has a first length andthe fluid distribution tube extends into the internal cavity by a secondlength that ranges between 50% and 100% of the first length.
 14. Thecatheter of claim 12, wherein the plurality of apertures of the fluiddistribution tube are arranged in a predetermined pattern.
 15. Thecatheter of claim 14, wherein the predetermined pattern includeslongitudinal alignment of the plurality of apertures.
 16. The catheterof claim 14, wherein the predetermined pattern includes a greaterspacing between more-proximal adjacent apertures and a lesser spacingbetween more-distal adjacent apertures.
 17. The catheter of claim 14,wherein the predetermined pattern includes the plurality of apertureshaving different radial positions in the side wall of the fluiddistribution tube.
 18. The catheter of claim 12, wherein the pluralityof apertures of the fluid distribution tube have different sizes. 19.The catheter of claim 12, wherein the plurality of apertures of thefluid distribution tube have different shapes.
 20. The catheter of claim12, further comprising an irrigation tubing in fluid communication withthe fluid distribution tube.